Polysaccharides or gums are primarily used to thicken or gel aqueous solutions and are frequently classified into two groups: thickeners and gelling agents. Typical thickeners include starches, xanthan gum, diutan gum, welan gum, guar gum, carboxymethylcellulose, alginate, methylcellulose, gum karaya and gum tragacanth. Common gelling agents include gelatin, gellan gum, starch, alginate, pectin, carrageenan, agar and methylcellulose.
Some polysaccharides, or more particularly stated, biogums, such as xanthan, gellan, welan and diutan have been produced via fermentation from microbes for many years. Such biogums exhibit varied characteristics such as viscosity modification capabilities that have permitted their utilization in many different applications. Included within such a list are gelling agents for foods, such as confectionery jellies, jams and jellies, dessert gels, icings and dairy products, as well as components of microbiological media. Furthermore, thickening agents are utilized for myriad end-use applications to modify the viscosity of target liquids. Of particular interest is the ability of such gums to impart viscosity modification to underground and/or underwater petroleum liquids to facilitate collection thereof, although many other different possible end-uses exist (including cement production, as one example). Different biogums have been produced from different bacterial sources, such as xanthan gum, from Xanthomonas campestris, gellan gum, from Sphingomonas elodea, welan gum from Sphingomonas sp. ATCC 31555, and diutan gum (S-657), from Sphingomonas sp. ATCC 53159. Genetic modifications of such strains have been undertaken in the past to effectuate significant changes in the resultant gum materials produced through the aforementioned fermentation procedures. Such modifications have permitted such changes as removal of acyl groups to create different gum materials exhibiting different physical properties. Generally, such genetic modifications have been of the type to either alter the composition of the target biogum ultimately through altered gene expression within the host organism, or increase the yield of the target biogum, through introduction of a plasmid that exhibits gene amplification alone (such as in U.S. Pat. Nos. 5,854,034, 5,985,623, and 6,284,516, to Pollock et al. and U.S. Pat. No. 6,709,845 to Pollock alone).
Diutan gum (also known as heterpolysaccharide S-657) is prepared by fermentation of strain Sphingomonas sp. ATCC 53159 and exhibits thickening, suspending, and stabilizing properties in aqueous solutions. Diutan generally exhibits a hexameric repeat unit consisting of four sugars in the backbone (glucose-glucuronic acid-glucose-rhamnose) and a side chain of two rhamnose residues attached to one of the glucose residues. Details of the diutan gum structure may be found in an article by Chowdhury, T. A., B. Lindberg, U. Lindquist and J. Baird, Carbohydrate Research 164 (1987) 117-122. Diutan was shown to have two acetyl substituents per repeat unit within Diltz et al., Carbohydrate Research 331 (2001) 265-270. Both of these references are hereby incorporated by reference in their entirety. Details of preparing diutan gum may be found in U.S. Pat. No. 5,175,278, which is hereby incorporated by reference in its entirety. Diutan may be produced from the Sphingomonas strain by utilizing standard fermentation techniques such as using carbohydrate sources (glucose, maltose, and the like, as non-limiting examples), a nitrogen source, and additional salts.
The physical characteristics imparted by such a diutan biogum in its wild-type form are desired by certain industries, particularly in terms of its viscosity modification properties and/or water retention characteristics. Unfortunately, diutan has proven difficult to produce cost effectively. Furthermore, such cost issues militate against widespread utilization of diutan currently since the degree of viscosity exhibited by such a biogum is insufficient to supplant other less expensive, but effective, biogums (such as xanthan gum, as one example). As such, it has been an established need to provide a method to produce such an effective diutan at lower cost, at the very least, and/or to provide a manner of producing a biogum of the diutan type that exhibits a significant improvement in physical properties as well. To date, the only mention of production of any types of related sphingans (without any demonstrations for diutan specifically) is in terms of higher yield (within the Pollock et al. patents mentioned above). There has been no discussion or fair suggestion of any manner of providing a method for producing an improved diutan gum of higher molecular weight that exhibits any improvement in viscosity measurements via such a production method.